[PATCH] i386: Convert i386 PDA code to use %fs

Convert the PDA code to use %fs rather than %gs as the segment for
per-processor data.  This is because some processors show a small but
measurable performance gain for reloading a NULL segment selector (as %fs
generally is in user-space) versus a non-NULL one (as %gs generally is).

On modern processors the difference is very small, perhaps undetectable.
Some old AMD "K6 3D+" processors are noticably slower when %fs is used
rather than %gs; I have no idea why this might be, but I think they're
sufficiently rare that it doesn't matter much.

This patch also fixes the math emulator, which had not been adjusted to
match the changed struct pt_regs.

[frederik.deweerdt@gmail.com: fixit with gdb]
[mingo@elte.hu: Fix KVM too]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Andi Kleen <ak@suse.de>
Cc: Ian Campbell <Ian.Campbell@XenSource.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Zachary Amsden <zach@vmware.com>
Cc: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Frederik Deweerdt <frederik.deweerdt@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index 359f10b54f59..11bf899de8aa 100644
--- a/include/asm-i386/processor.h
+++ b/include/asm-i386/processor.h
@@ -424,7 +424,7 @@ struct thread_struct {
         .vm86_info = NULL,                                              \
         .sysenter_cs = __KERNEL_CS,                                     \
         .io_bitmap_ptr = NULL,                                          \
-        .gs = __KERNEL_PDA,                                             \
+        .fs = __KERNEL_PDA,                                             \
 }
 
 /*
@@ -442,8 +442,8 @@ struct thread_struct {
 }
 
 #define start_thread(regs, new_eip, new_esp) do {               \
-        __asm__("movl %0,%%fs": :"r" (0));                      \
-        regs->xgs = 0;                                          \
+        __asm__("movl %0,%%gs": :"r" (0));                      \
+        regs->xfs = 0;                                          \
         set_fs(USER_DS);                                        \
         regs->xds = __USER_DS;                                  \
         regs->xes = __USER_DS;                                  \